For a Machine Type Communications (MTC) project, a method for repeated transmission in a plurality of subframes in a physical channel has been proposed so as to enhance the coverage of a MTC device in a deep-fading scenario. In order to achieve the coverage enhancement up to 15 dB, the repeated transmission may be performed for dozens or hundreds of times. Currently, there is no conclusion about how to determine a redundancy version during a repeated transmission period.
In the related art, for downlink data transmission, transport blocks arrived within a Transmission Time Interval (TTI) are processed by an encoding unit, and then by the physical channel, and then transmitted on a corresponding physical resource. As shown in FIG. 1, the transport blocks from a Media Access Control (MAC) are processed by the encoding unit and the physical channel, and then transmitted in subframes (e.g., subframe #0 of radio frame #M, subframe #2 of radio frame #M+1, and subframe #3 of radio frame #M+2). In the TTIs, the transport blocks are processed independently.
A processing procedure of the transport block includes a rate matching procedure which includes sub-block interleaving, bit collection and bit selection. As shown in FIG. 2, during the bit collection, a system bit stream, a first check bit stream and a second check bit stream processed by a sub-block interleaver are cascaded. During the bit selection, an output bit stream is selected based on the redundancy version (RV=0, RV=2, RV=3 and RV=1) of the subframe. For the downlink data transmission, the redundancy version is indicated in Downlink Control Information (DCI).
For uplink data transmission, there are two modes, i.e., a single-subframe transmission mode and a TTI bundling mode. For the single-subframe transmission mode, a procedure is substantially similar to that for the downlink data transmission. The transport block within each TTI is processed by the encoding unit and then processed on the physical channel, and then transmitted on a corresponding resource. The transport blocks in the TTIs are processed independently.
The redundancy version for the uplink data transmission is determined by a parameter CURRENT_IRV at an MAC layer, and this parameter is used to indicate a serial number in a redundancy version sequence. After the transmission (the transmission for the first time or retransmission) of a Hybrid Automatic Repeat Request (HARQ), CURRENT_IRV is incremented by 1. In addition, CURRENT_IRV is subjected to a modular four operation, and the redundancy version sequences are 0, 2, 3 and 1.
An uplink TTI bundling mode is used to enhance the uplink coverage, and different redundancy versions for one transport block are transmitted in a plurality of consecutive subframes (TTIs), i.e., the HARQ retransmission is performed automatically in a plurality of consecutive TTIs. During the HARQ retransmission, it is unnecessary to feed back any Acknowledgement (ACK)/Non-Acknowledgement (NACK). As shown in FIG. 3, after a Cyclic Redundancy Check (CRC) operation, a channel encoding operation and a rate matching have been performed on the transport block from the MAC layer, different redundancy versions for the transport block are transmitted in the plurality of consecutive TTIs. For example, four redundancy versions, i.e., RV=0, RV=2, RV=3 and RV=1, for each transport block are transmitted in FIG. 3.
However, in order to reduce the retransmission times as possible, thereby to prevent the decrease in the system spectral efficiency due to the retransmission as possible, after study, cross-subframe channel estimation has been proposed as an effective measure. The so-called cross-subframe channel estimation refers to joint channel estimation performed based on reference signals in a plurality of consecutive subframes using channel correlation. As a typical processor mode, a weighted averaging operation is performed on results of the channel estimation in the plurality of subframes. Correspondingly, coherent combination is performed on data sections on the premise that signals transmitted in the plurality of subframes for the coherent combination are identical to each other.
However, in the related art, for the downlink data transmission, the transport blocks in the TTIs are processed independently, and there is no mechanism in which one transport block is repeatedly transmitted in the plurality of subframes. For the uplink data transmission, one transport block may be repeatedly transmitted in the plurality of subframes through the TTI bundling mechanism, but the redundancy versions recurrently vary along with the subframes, i.e., the redundancy versions in adjacent subframes are different from each other. This means, the signals transmitted in the subframes are different from each other after the rate matching, so it is impossible to perform the coherent combination on the signals at the receiving end.
In a word, in the related art, during the retransmission of the information in the plurality of subframes, the redundancy versions recurrently vary along with the subframes, and the redundancy versions in the adjacent subframes are different from each other. At this time, the information transmitted in the subframes after the rate matching is different, and thereby, at an opposite end, the information received in the plurality of subframes for the coherent combination is different too. Hence, it is impossible to prevent the decrease in the system spectral efficiency due to the information retransmission.